The invention relates to a device for printing a sign at a predetermined location on one face of a flat object having a thickness lying within a given range.
It is known that this type of device is found especially in franking machines, the sign to be printed being the franking mark.
It has already been proposed, especially in the French patent application 97 09888 (2 766 757), to provide an abutment element for the face of the object to be printed, to move the object with its face to be printed which is flush with this element, and to deposit the sign to be printed while the object is moving, by virtue of an ink jet cartridge which can be used since the abutment element makes it possible to keep constant the distance between the ink spray nozzle and the location of the object where the sign is to be printed, despite the variations in thickness from one object to another as well as the disparities in thickness which the same object may exhibit.
The invention aims to furnish such a device featuring good performance as far as print quality is concerned.
To that end it proposes a device for printing a sign at a predetermined location on one face of a flat object having a thickness lying within a given range, including an abutment element for the face of the flat object to be printed, drive means for moving the object along the abutment element with its face to be printed which is flush with this element, and printing means including means for depositing the said sign at the said predetermined location while the object is moved by the drive means along the abutment element, the said drive means including a non-suspended support means for the face of the said object to be printed, and including a belt featuring a stretch facing the said support means and extending between an upstream roller and a downstream roller which are suspended in such a way that the said object can be sandwiched between the said non-suspended support means and the said stretch of the belt; characterized in that the said belt is wound around at least two other rollers, at least one of which is not suspended.
The presence of these other rollers is favorable for maintaining tension in the belt and thus for the constancy of the speed of movement of the stretch in contact with the object, which makes it possible to obtain good regularity for the printing of the sign.
According to preferred characteristics, at least one of the rollers around which the said belt is wound is driven in rotation.
The belt is thus put into movement by one of the rollers about which it is wound, which is favorable to the constancy of its speed and thus to the regularity of the printing of the sign.
In particular, the regularity of the speed is better than in the device described by the abovementioned patent application, in which the belt is driven by external counter-rollers on which the upstream roller and the downstream roller respectively bear, the conditions of contact between the belt and these rollers being altered during suspension movements of the upstream and downstream rollers.
For reasons of production convenience, it is the said other, non-suspended roller which is preferably driven in rotation.
According to other preferred characteristics, the device according to the invention includes an arm carrying the journal of one of the said upstream rollers and downstream roller while the said arm is mounted so as to oscillate on the journal of the said other non-suspended roller.
The guidance of the suspension movement of the upstream roller and/or of the downstream roller obtained by virtue of this arm in effect makes it possible to obtain good maintenance of the tension of the belt.
The said arm preferably extends downstream from the said journal on which it is mounted so as to oscillate.
According to other preferred characteristics, for the reasons which have just been set out, each of the said other two rollers is not suspended and each of the said upstream roller and downstream roller is carried by a respective arm mounted so that it can oscillate on the journal of a respective one of the said other two rollers.
According to other preferred characteristics, the said belt is wound around three other said rollers, respectively a first non-suspended roller, a second non-suspended roller and a third suspended roller.
The presence of this third other roller makes it possible to obtain particularly good regularity of the speed of movement of the belt.
The said third suspended roller is preferably suspended dependently from one of the said upstream rollers and downstream roller, such that, if this latter has a suspension movement of such a nature as to slacken the said belt, the suspension movement of the third roller is of such a nature as to re-tension the said belt.
Also preferably, for practical reasons of size, the said third roller is suspended dependently from the said downstream roller.
According to other preferred characteristics, the device according to the invention includes an arm mounted so that it can oscillate at its center on the journal of the said other non-suspended roller, the said arm carrying, at one end, the journal of one of the said upstream roller and downstream roller, while at the other end it carries the journal of a said second other roller.
Hence, any slack due to the suspension movement of the upstream or downstream roller is taken up by the second other roller, the angle of winding of the belt on this second other roller is preserved at least approximately during suspension movements, which is particularly beneficial when the second other roller is driven and, which is also particularly beneficial in this case, the second other roller is in contact with the belt via the face thereof which is intended to come into contact with the object, in such a way that advantage is taken, for driving the belt, of any anti-slip character of this face.
According to other preferred characteristics, the said non-suspended support means is formed by the stretch of a second belt extending between two non-suspended rollers, positioned in a predetermined way with respect to the said abutment element.
By virtue of these characteristics it is possible to obtain excellent printing results, especially if the two belts are driven synchronously at the same speed.
According to other preferred characteristics:
the said second belt is wound exclusively around non-suspended rollers;
two of the said non-suspended rollers around which the said second belt is wound serve as a counter-roller respectively for the said upstream roller and for the said downstream roller;
the same motor serves to drive the said belt and second belt;
the said abutment element is offset laterally with respect to the said support means;
the said abutment element is arranged between the said support means and a lateral abutment means for the said object to be franked; and/or
the said printing means include at least one ink jet cartridge equipped with a head for sending ink onto the said predetermined location of the object, from a recess in the abutment element.
According to a second aspect, the invention also envisages a franking machine including a device as set out above, for printing a franking mark.